The National Investigation Agency has arrested Muslim Khan, an alleged conspirator in the brutal killing of a tailor in Rajasthan's Udaipur, making it the ninth arrest by the central agency in the case, officials said.

The agency said 41-year old Khan alias Muslim Raza, a resident of Pratapgarh in Rajasthan, played an "active role" in the conspiracy.

The National Investigation Agency (NIA) has made nine arrests in the case since taking over the probe on June 29, with the last arrest made on July 21 when Mohammad Javed, a resident of Sindhi Sarkar Ki Haweli, Kheradiwala, was taken into custody.

The tailor Kanhaiya Lal was killed with a cleaver inside his tailoring shop in Rajasthan's Udaipur on June 28. The gruesome attack by Riaz Akhtari on the tailor was recorded on a mobile phone by Ghouse Mohammad and the video was posted online.

In another video, the duo said they hacked Lal to death to avenge an alleged insult to Islam. Both were arrested within hours of the killing.

The NIA said the two wanted to "strike terror among the masses across the country" through the gruesome act. The duo had posted videos online claiming responsibility for the attack and also issued a threat to Prime Minister Narendra Modi. it said.

Officials said the agency is looking into the role of "local self-radicalised gangs" and their possible international linkages, even as a preliminary probe suggests that more people could be involved in the conspiracy to murder Lal.

NIA officials said the two became members of Pakistan-based Sunni Islamic organisation Dawat-e-Islami via a mobile application and one of them was in touch with some people in Pakistan. They, however, said it was too early to draw any conclusions.

The Karachi-based Dawat-e-Islami website, however, says it is a "global non-political Islamic organisation working for the propagation of the Quran and Sunnah throughout the globe" and that it was established in 1981.